DavidR
12
System Restore can have unforeseen consequences one seems it messes with avast as it ends up with old files.
You can have the license resent:
Resend avast License http://www.avast.com/resend-license-paid.php, you will need to enter the email that you used when purchasing the license, e.g. the one that the original email with the link was sent.
So you should be able to reinstall, but you really should backup your data and that would include things like your avast license file license.avastlic and other registration keys, etc.